Agricultural vehicles such as tractors, combines and the like are commonly used in agricultural fields for a variety of jobs, and construction vehicles and other large work vehicles are used for many different jobs on a variety of ground surfaces. Typically, these vehicles have large wheels with tires on which the vehicles are supported on the ground. However, for improved traction, vehicle-track module systems or, more broadly, track assemblies are used in place of wheels with tires, and such track modules and track assemblies provide a much larger ground-surface engagement area that spreads vehicle weight and tends to prevent vehicles from becoming bogged down in mud or other soft ground surfaces.
Track assemblies for a vehicle typically include a frame mounted with respect to the vehicle and a plurality of wheels in contact with a continuous flexible track which extends about the plurality of wheels. More specifically, a track module, which is a type of track assembly, for use in modular tracked vehicles typically has a upper drive wheel connectable with respect to a vehicle axle for rotation therewith, a plurality of idler and bogie wheels, and an endless flexible rubber track with a main inner surface and spaced track lugs projecting inwardly therefrom, the track extending around the wheels and being driven by its engagement with the drive wheel. Such drive wheels may be large and may, of course, have circumferentially-spaced drive members engageable with the track lugs.
Use places enormous strain on the mechanics of the track assembly, particularly with respect to the wheels, the flexible track around the wheels, and the lugs on the track. This wear-and-tear on the track is especially pronounced in circumstances where a vehicle with a track assembly is driven on a surface that is not substantially level, a scenario often encountered in both the construction and agricultural fields of use. On crowned roads, for example, the bulk of the weight of the vehicle is not evenly distributed across the entire width of the track. Rather, depending upon the type of crowned road, the vehicle load may be primarily distributed toward the outer edges of the track, which, of course, is not desirable because this will cause premature track wear shortening the useful life of the track.
The term “crowned” describes the cross-sectional shape of a road surface and the term “cross slope” describes the slope of a road surface perpendicular to the centerline of the road. There are several types of crowned roads. For example, a road may have a centerline crown in which case the road slopes down and away on both sides from a road surface center point. A normal crowned road has a small degree of cross slope that would ordinarily be imperceptible to a person driving a vehicle thereon. Crowned roads may, however, have a more significant degree of cross slope. Such a road may look rounded in the middle. In a rounded crowned road, the center of the road may be flat, in which case the road slopes down and away from the center flat portion of the road on both sides. Older rural roads, whether paved or unpaved, typically include some form of a centerline crown. In some instances however, especially seen in narrower roads, a crowned road may slope primarily more toward one side of a road surface than the other. For example, a road may slope toward a down-slope side of a road toward a road shoulder or, conversely, a road may slope down and toward an up-slope side of a road toward a road shoulder.
Track modules and assemblies seen in the prior art are not especially suited for use on crowned roads having variable degrees of cross slope because the wheels themselves on such known vehicle track modules are not generally compliant and, thus, do not accommodate for the slope in the road. Some modules and assemblies may attempt to compensate surface cross slope by including roll axis structure for the wheel shafts. A roll axis allows the wheels to move up and down around an axis substantially parallel to the direction of vehicle motion in response to irregularities in a ground surface. Including a roll degree-of-freedom for a wheel axle adds additional complexity and cost to the structure of the vehicle track module. It also adds additional structure subject to wear and failure and requiring the need for regular maintenance, repair and replacement.
A solution to the problems described above which still retains the advantages of track-assembly technology and which accommodates variability in road-surface cross slope and reduces uneven track wear would be an important advance in the art.